C Springer-Verlag Berlin Heidelberg 2007 Model-Based Diagnosability Analysis for Web Services 25 type of analysis depends on the speciﬁc formalization of the notion of diagnosis that is being used for on-line software. In this paper we analyze the problem of diagnosability, with respect to the formalization of diagnosis introduced in [2] and the algorithm described in [1]. Before giving a short description of this framework, it is worth pointing out some peculiarities of the WS scenario, that pose some interesting problems with respect to existing literature on diagnosability analysis.

2 We will consider in this context that the “all ok” state is one of the possible fault modes. 28 S. Bocconi et al. Since, depending on the particular situation, many of these properties can be of interest for the designer of a composite WSs, we prefer to focus on the notion of discriminability, which is given with respect to a pair of fault modes: Deﬁnition 1 (Discriminability). Two fault modes are discriminable if their patterns of observable values are disjoint. Since we consider relational models, this means that two fault modes f1 and f2 are discriminable if the portion M (f1 ) of the global model consistent with f1 , and the one (M (f2 )) consistent with f2 , are disjoint when projected on observable variables.